Abstract
The measurement of unsteady or tidally affected flow has been a problem faced by hydrologists for many years. Dynamic discharge conditions impose an unreasonably short time constraint on conventional current-meter discharge-measurement methods, which typically last a minimum of 1 hour. Tidally affected discharge can change more than 100 percent during a 10-minute period. Over the years, the U.S. Geological Survey (USGS) has developed moving-boat dischargemeasurement techniques that are much faster but less accurate than conventional methods. For a bibliography of conventional moving-boat publications, see Simpson and Oltmann (1993, page 17).
The advent of the acoustic Doppler current profiler (ADCP) made possible the development of a discharge-measurement system capable of more accurately measuring unsteady or tidally affected flow. In most cases, an ADCP discharge-measurement system is dramatically faster than conventional discharge-measurement systems and has comparable or better accuracy. In many cases, an ADCP dischargemeasurement system is the only choice for use at a particular measurement site.
ADCP systems are not yet “turnkey”; they are still under development, and for proper operation, require a significant amount of operator training. Not only must the operator have a rudimentary knowledge of acoustic physics, but also a working knowledge of ADCP operation, the manufacturers' dischargemeasurement software, and boating techniques and safety.
The purpose of this report is to describe ADCP operating techniques, fundamental ADCP theory, ADCP discharge-measurement theory, and vessel mounts and operating techniques required for ADCP discharge measurements. It is not intended to replace the “hands-on,” USGS-approved training required for all ADCP discharge-measurement system operators. This report only describes the Microsoft Disk Operating System (MS DOS) version of the dischargemeasurement software, Transect, and will have to be revised to include future versions that run under Microsoft Windows. The report also only describes the configuration and use of the R.D. Instruments, Inc. (RDI), broad-band ADCP (BB-ADCP). Subsequent modifications to the BB-ADCP will be included in updates to this report if these modifications significantly change the configuration of the ADCP or if discharge-measurement techniques must be changed. This report also will be updated if another manufacturer’s ADCP is used to measure discharge by a significant number of USGS users.